Macbook Air Trade-in Value

Is this a third party company you sent it to? Did you take detailed photos of the condition of your device before mailing it in? That would be recommended; there have been reports about greatly reduced final offers. If you have any proof that yours did not have that problem, I would challenge the company directly and submit my proof. If you do not, there isn't much you can do - you can call Apple's attention to it, but I do not know what clauses their agreement contains.

I'd probably tell them to send it back in the same condition it was in and then would sell it myself. But tell them you want to see proof of the delamination they are claiming. FWIW, I would not use any of those third party companies unless I had definitive proof of the perfect condition of my device and then question them. I'd rather sell it myself.